Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $61.44   11.860%   $68.7268   $68.73   $68.75   $68.70  
  Purchase #2 $236.97   4.822%   $248.3967   $248.40   $248.40   $248.40  
  Purchase #3 $110.93   11.521%   $123.7102   $123.71   $123.70   $123.70  
  Purchase #4 $178.91   7.390%   $192.1314   $192.13   $192.15   $192.10  
  Purchase #5 $227.72   13.787%   $259.1158   $259.12   $259.10   $259.10  
  Purchase #6 $87.36   8.182%   $94.5078   $94.51   $94.50   $94.50  
  Purchase #7 $42.72   8.138%   $46.1966   $46.20   $46.20   $46.20  
  7 purchase totals = $946.05       $1,032.7853   $1,032.80   $1,032.80   $1,032.70